Copper foil for use in the manufacture of copper-clad laminates used in making printed circuit boards (PCB's) is usually made on a rotating drum cathode machine. In this method copper is electrodeposited on a rotating cylindrical drum cathode by passing an electric current from a lead, or lead-antimony, anode (usually two anodes) through a copper-containing electrolyte such as, an aqueous copper sulfate/sulfuric acid solution, to plate copper on the surface of a rotating drum cathode partially immersed in the electrolyte. The drum cathode typically has an outer top sheet formed of titanium or a similar metal. As the drum rotates, copper is plated onto the outer surface of the top sheet, and a web of raw copper foil is continuously stripped from the drum surface and coiled. Such stripping is possible because the top sheet of the drum is made of a metal such as titanium, which provides a low adhesion between the plated copper foil and the surface of the top sheet.
The thickness of the copper foil plated on the drum cathode is determined by a number of variable process parameters, and it is known to produce thin copper foil and ultra-thin copper foils, i.e., one-half ounce or less foils (those having a normal thickness of about 17 microns nominal thickness or less). However, the production efficiency of electrodeposited copper foil, especially ultra-thin copper foil, is reduced by a tendency for the raw foil to tear during the course of the processing. This problem is especially severe when very thin foil is being stripped from the drum cathode. This tearing problem makes the production of copper foil having a nominal thickness of 12 microns, or especially 9 micron foil, extremely difficult and uneconomical due to the extremely low production yields.